Equisignal radio beacon system



May 31, 1949. w. J. OBRIEN EQUISIGNAL RADIO BEACON SYSTEM Original Filed March 2; 1942 2 Sheets-Sheet 1 Pmst' Smrrm Joana- 0112/."

INVENTOR lV/LL/AM of Uflfl/EN,

BY 2 JTEOk/VEY.

' May 31, 1949. W.'J. OBRIEN I EQUISIGNAL RADIO BEACON SYSTEM 2 Sheets-Sheet 2 Original Filed March 2, 1942 FIG. 4.

15 Fla 7 IINVENI'OR lV/zzmu r/I 030/54 Patented May 31, 1949 EQUISIGNAL RADIO BEACON SYSTEM William J. OBrien,

London, England, assignor to The Decca Record Company, Limited, London, England, a corporation of Great Britain Original application March 2, 1942, Serial No.

432,948. Divided her 8, 1943, Serial 9 Claims. 1

My invention relates to a radio beacon system and has particular reference to an equi-signal type of radio beacon which finds particular utility when employed as a navigation aid for vehicles and conveyances, particularly aircraft.

This is a division of my copending application Serial No. 432,948, filed March 2, 1942, and entitled Equisignal radio beacon systems (now Patent No. 2,406,396).

The equi-signal type of radio beacon system is that which is at present employed in the United States Department of Commerce airways radiorange beacon for establishing the transcontinental air routes followed by the commercial air transport companies. This type of system generally comprises a group of radio transmission antennae so arranged and so operated that the course along which it is desired to navigate an aircraft comprises the locus of points of equal signal intensities as regards separate signals of like frequency emanated from the antennae. In general, these separate signals are reciprocally and distinguishably keyed off and on, the conventional arrangement being that in which one signal is keyed with the International Morse Code character for A while the other is alternately keyed N If the aircraft is on course the intensities of the two signals are equal and the off periods of one coincide with the on periods of the other so that a steady and continuous signal is received. If the plane is off course, one of the signals will predominate over the other and the keying of the signals will be apparent. The direction in which the plane has drifted from the course is indicated by whether the A or N signal predominates.

The present systems while of great assistance in the navigation of aircraft, nevertheless are characterized by certain disadvantages and difficulties. For example, the present systems do not provide a sufficiently sensitive indication to permit their successful application to long range control, as for example, the guiding of bombing planes in war time to an objective to be bombed situated five or six hundred miles distant. The sensitivity of the present system can be increased by increasing the antenna spacing. There are, however, practical limitations on how far apart the antennae may be successfully spaced and, furthermore, an increase in antenna spacing likewise increases the number of equisignal courses produced so that the danger of an aircraft becoming lost through inability to identify the course is correspondingly increased.

It is, therefore, an object of my invention to and this application Novem- No. 509,445

provide an equi-signal type of radio beacon system which overcomes the above noted disadvantages by providing for increased sensitivity of indication.

It is an additional object of my invention to provide a radio beacon system of the character set forth in the preceding paragraphs which is characterized by a novel and simplified keying arrangement for producing the on course and ofi course signals.

Other objects and advantages of my invention will be apparent from a study of the following specifications, read in connection with the accompanying drawings, wherein:

Fig. 1 is a diagrammatic view illustrating by means of curves drawn on a polar coordinate system the relative signal intensities produced by two radio transmission antennae when operated as hereinafter described, and illustrating also the manner in which these separate signal intensities operate to define an equi-signal course;

Fig. 2 is a diagrammatic view illustrating the mode of operation of the two antennae indicated in Fig. 1, and illustrating also the way in which such operation produces an indication of the location of a vehicle with respect to the course defined by the system;

Fig. 3 is a diagrammatic view representing a suitable type of receiving apparatus;

Fig. 4 is a polar diagram similar to Fig. 1 but illustrating the result of operating the antennae A and B by a different mode of operation;

Fig. 5 is a diagrammatic view illustrating the manner in which the antennae. A and B are operated, and illustrating also the manner in which the system operates to indicate to the pilot of a vehicle the location of the vehicle with respect to an equi-signal course defined by the beacon system;

Fig. 6 is a vector diagram illustrating the manner in which the signals alternately produced by the system illustrated in Fig. 4 serve to produce suitable indications of the location of the vehicle with respect to the desired course; and

Fig. 7 is a diagram showing one form of transmitting apparatus which may be used in the practice of the invention.

Referring to the drawings, I have illustrated in Fig. 1 two radio transmission antennae A and B as being spaced from each other a known distance. Fig. 1 illustrates by means of the solid line curve A+B the field pattern which is produced when the antennae A and B are spaced apart a distance corresponding to one wavelength and are operated simultaneously in phase and at identical frequencies. The dotted circle A in Fig. 1 represents the field strength produced when the antenna A is alone excited.

These two field patterns operate to define a plurality of equi-signal courses along which the signals emanated *from antenna .-'A valone are equal in intensity to the combined signals emanated by the simultaneous operation of antennae A and B. One such course is indicated by the dashed arrow l in Fig.1 It will be,noted this course extends from an originOdisposed-on a line extending through theeantennae. A-and'B midway between said antennaesan'dtthrougha point 2 comprising the intersectiomofthe.curve A+B with the circle A. Atany .point along the on course line I the signals A-l-B are equal in intensity to the signal produced by the operation of antenna A alone.

This phenomenon may be employed toguide a vehicle or conveyance such as an aircraft to a chosen destinationby. so .pcsitioning the antennae A an'd"B,that.the. equi=signalline1 extends through the...selected destination .and by providing the vehicle with suitable radio'receiving apparatus tuned.to.-.receive the-signals emanating iromthe antennaeA and..B. v.Such a receiving apparatus.is diagrammaticallyillustrated in Fig. 3 as. comprising arconventional radio frequency receiverJ-S .providedmith an. antenna 4 for receiving the radiation from the-antennae A and B and coupled to asuitable indicating: device: such as a loud ,speakermr.-headphoneslS. It is preferred to transmit ifmm..antennae A..and .3 .unmodulated signals .and-jo .provide a beat .frequency oscillator];.which.is.,so..coupled to-the receiver 3 as toproduce inltheheadphones 5 an audible beat.note..resulting ,fromreceiving the signals from either. of .the. antennae .A. and B.

In order. forthe. pilot ondriver .ofthe vehicle to be able to ascertainwhether orinot' he is proceeding along one of.the equ-i-.-signal .courses' such-as the course lit .is'necessarsfito. provide .some means permitting him to identify".those. changes in the relativeamplitudes..of-.the-'two types of signals received which result {fromthe .deviation of the vehicle from,the..;selected.course. "Ilhave illustrated in Fig. 2 theumanneriinwhich this result can be achieved .by appropriate -control of the radiation of energy, from the antennae. AandLB.

Fig. 2 comprises afrectangularjidiagram in which the uppermost portion' illustrates themode of operation of one ofthe antennaasuchmas antenna A. This antenna is operatedrontinuously and without .interruption. .Aritennai'Bais, however, preferably keyed ,off and ion".asflillustrated.by the central portionof "Fig.1.2. Preferably the "on periods aresubstantiallythree timesas-long as the off perio'ds. The.lowermost.portion of Fig. 2 indicatesthe'type of signal which is,provided inthe headphones 5.

By referringto'Fig. 1' it'will be-noted that when the vehicle is .on..course,.lthe signals .emanating from the antennaJA. during the o periods of the antenna .3 operation are ,equal'in intensity to the signals resulting from the simultaneous operation ,of antennae. A.and.'B. QThusthere is received in the headphones 5a .steady..-and .unchanging. signal such .that indicated by the straighthorizontallinel.in.that;.portion of. Fig. 2 bounded-by-.the-wavy..break1lines .8 and .9. .If, however, thevehicle deviates the .left of .the equi-Signal. course). I ,so -as.to .followa: course. such as. that, for example, indicatedbytthe dotted line lllinFig. l, thesignal -which is emanatedsfrom antenna A alone :willypredominate in intensity over the signals produced by the simultaneous operation of antennae A and B.

The signal thus reproduced by the headphones 5 is illustrated diagrammatically in Fig. 2 and particularly in that portion lying to the left of the wavy break line 8. 'By reference to this portion of Fig. 2, it will be noted that the A signals predominate over the A-l-B signals and that the A signals have a time duration which is material ly .less thanthe duration of the A-l-B signals. This renders the signals distinguishable b the pilot of the vehicle and such a pilot obtains the impression of hearing a series of spaced dot si nals. Conversely, if the vehicle deviates to the right of the equisignal course I as, for example,

.along a. course indicated by the dotted line I l in Fig. 1, the signals produced by the simultaneous operation of antennae A and B will predominate in intensity over the signals resulting from the operation of antenna A alone.

This condition is illustratedin Fig. 2 in that portion lying tothe right of the Wavy break line El. By reference to this portion of Fig. 2 it will be noted that the A-l-B signals not only predominate in intensity over the-Asignals, but also are characterized by a time .duration materially greater than the duration ofthe "A signals. The pilot of the vehicle thusobtains-the impression of hearing in the headphones ia series of dash signals.

Summarizing the foregoing it will be seen that the on course condition is indicated by a steady tone, whereas, a -series.of ,-space.d dot signals indicates that the-vehicle vis-to the left of the selectedcourse, whereas, a series of spaced dash signals indicates-that the vehicle is to the right of the selected course.

I have illustrated-inFig. .4 .amodified equisignal beacon system in which the antennae A and B, while spaced -.as.in Fig. 1, namely, at a distance corresponding to. one wavelength of the radio vfrequency energy radiated from the antennae, are so operated.thatthexsignals of one lead the other by electrical degrees. This change in the phase relation between the signals emanated from the antennae A andB serves to shift the equi signal course angularly to a position extending at rightangles to the line joining the antennae A andB, such shifted.equi-signal course beingindicated .by the dashed arrow 12 in Fig. 4.

.By comparing .Figs. land 4 the manner in whichthe compassadirectionof the equi-signal coursecan'be changed by'merely changing the phase relation between the signals emanated from the antennae Aand-B is seen. As in Fig. 1, the solid curve in Fig. 4 illustrates the field strength .pattern produced by thesimultaneous operation of the antennae A.=and.B, whereas, the dotted circle illustrates the vfield pattern producechby theoperation of .oneof the antennae alone. With this form ofthe invention I preier vtoemploy the same type of. receiving equipment as, described in connection withFig. 1.

While I have-describedthe-spacing oftransmitters A and .B as being .one wavelength, it is to be understood that .this spacing has .been chosen for illustrative .purposes only and that other spacings may.be.used as desired. However, I prefer to .limit. theproximity of the sta tions to at least one-half wavelength so that the number of equi-signal surfaces produced by the system will difier-by n-o-more than one from that number equalling eight times the spacing in wavelengths of the transmittingwantennae. A

spacing closer than one-half wavelength produces a pattern having an undesired kidney bean shape.

Fig. 5, however, illustrates a different mode of opera-tion of the antennae A and B for producing the desired indication of the location of the vehi-cle with respect to the equi-signal source l2. As is indicated by the uppermost portion of Fig. 5, antenna A is pref-erbly keyed off and on in such manner that the duration of the periods of energization of the antenna exceed the periods of de-en-ergization. As is shown by the central portion'of Fig. 5, antenna B is similarly operated but in staggered time relation to antenna A so as to provide three distinct periods of operation; namely, one in which antenna A alone is operated, another in which antennae A and B are simultaneously operated, and a third in which antenna B alone is operated.

When the vehicle is moving along the equisignal course l2 a steady tone is produced in the headphones 5 by virtue of the fact that the si nals resulting from the operation of antenna A alone, the operation of antenna B alone and the simultaneous operation of antennae A and B are all equal as indicated by the straight horizontal line l3 included in the lower portion of Fig. 5 between the wavy break lines I 4 and I5.

' By reference to Fig. 4 it will be noted that should the vehicle wander to the left of the course [2 as, for example, along a course such as that indicated by the dotted arrow l6 in'Fig. 4, the signal received during the simultaneous operation of antennae A and B will predominate in intensity over the signals received from antennae A or B alone. By referring to that por tion of Fig. 5 lying to the left of the wavy break line l4, it will be noted that the A+B signals exceed in intensity the A signals and the B signals.

.As is clearly illustrated therein, the keying of the A and B antennae is so arranged that the duration of the periods of simultaneous operation of the antennae is approximately one-third the duration of the periods in which each antenna is operated alone. Thus, the predominance of the relatively short A+B signal provides the pilot with the impression of hearing a series of spaced dot signals.

By reference to Fig. 4 and that part of Fig. 5 lying to the right of the wavy break line I5, it will be noted that the conditions are reversed when the vehicle wanders to the right of the course as, for example, along the course indicated by the dotted arrow I! in Fig. 4. Under these circumstances the A and B signals predominate in intensity over the A+B signals and also have a duration substantially three times the duration of the A+B signals so that the pilot of the vehicle receives the impression of hearing a series of spaced dash signals. The indication given the pilot is thus the same as that given by the system described in connection with Figs. 1 and 2.

Fig. 6 is a vector diagram illustrating the phase relationships between the signals which are responsible for the shift in predominance of the signals as the vehicle wanders from one side to the other of the selected course. It will be noted that any selected point on the equi-signal course I2 is equally distant from the antennae A and B so that the signals received at such point from these separate antennae bear the same phase relationship to each other as do the signals emanating from the antennae.

As before noted, the phase relation illustrated in Fig. 4 is that in which the signals emanated from antenna B lead the signals emanated by antenna A by electrical degrees. This condition is illustrated by the vectors A2 and B2 in Fig. 6. The sum of these vectors is indicated by the vector bearing the reference character (A'Z-l-BZ). It will be noted that this resultant vector is equal in length to the vectors A2 and B2 so that signals emanated from antenna. A or antenna B are indistinguishable from the signal produced by the simultaneous operation of these antennae.

When the vehicle is moved to the left of the course l2 as, for example, to the course I 6, the distance from the vehicle to the antenna A is shortened with respect to the distance to the antenna B so that at the location of the vehicle the B signals lead the A signals by an electrical angle less than the angle by which the signals emanated at the antenna B lead thesignals emanated at the antenna A. This condition is illustrated by the vectors A3 and B3 in Fig. 6, the resultant of which is illustrated [by the vector (A3+B3) which, it will be noted, has a magnitude considerably greater than that of the signals A3 and B3.

Similarly, a shift of the Vehicle to the right of the equi-signal course l2 increases the phase angle between the signals, in which case the signals may be represented by the vectors Al and BI in Fig. 6. The sum of these vectors is indicated by the vector (AI+Bl) which, it will be noted, discloses a magnitude materially less than the magnitude of the signals A! and BI.

I have diagrammatically illustrated in Fig. 7 one form of apparatus which may be used to energize antennae A and B as hereinbefore described and Which may include a suitable source 20 of radio frequency energy. The source 20 is coupled to a pair of cam-operated switches 2| and 22 arranged to be driven by a clockwork 23 or other suitable timing mechanism, the cam operator for the switches :being arranged to open and close the switches 2| and 22 in accordance with the time cycle hereinbefore described. The switch 2| serves to periodically connect the source 20 to antenna A through a transmission line 24 and antenna coupling 25. The switch 22 serves to periodically connect the source 20 to antenna B through a phase shifter 26, transmission line 21 and antenna coupling 28. The phase shifter 26 is used to adjust the phase of the signals radiated from antenna B with respect to those radiated from antenna A for the purpose of adlusting the orientation of one or more of the equi-signal courses as hereinbefore explained.

In the foregoing, I have illustrated and described an improved form of equi-signal radio beacon system which is characterized particularly by its simplicity, ease of operation, and high degree of accuracy and sensitivity attained.

While I have shown and described the preferred embodiment of my invention, I do not desire to be limited to any of the details of construction shown or described herein, except as defined in the appended claims.

I claim:

1. The method of producing a radio frequency equi-signal surface for guiding mobile vehicles which consists in radiating radio frequency signals of like frequency from a pair of spaced points, and producing each of said signals intermittently in substantially identical repeating cycles of off and on periods with the on periods of one signal overlapping the on periods of the lotliersignal for a time tialifraction of the duration of said periods.

nals of like frequency from of .one signal "other signal to such an extent that the time .equi-signal surfaces for .ing radio frequency 'nal surfaces, and adjusting the relative the on periods of one periods of the other signal to such an extent that .the duration of the constituting a-substan- 2. The method of producing a radio frequency equi-signal surface for guiding mobile vehicles which-consists in radiating radio frequency siga pair of spaced points, and producing each of said signals in- 'termittently in substantially identical repeating cycles of off and on periods with the on periods overlapping the on periods of the duration of the periods in which both signals are radiated is a substantial fraction of the time duration of said periods and materially different from the duration of the periods in which one signal only is radiated.

3. The method of producing radio frequency guiding mobile vehicles in any desired direction which consists in radiatsignals from a first position, periodically radiating radio frequency signals from a. second position spaced from said first position a distance of at least one-half wavelength plurality of equi-sigphase of to extend one of said equiof'said signals to produce a said radiated signals signal surfaces in said desired direction, whereby the number of equi-signal surfaces so produced differs by no more than one from that number equalling eight times the spacing in wavelengths of said radio frequency signals of said vfirst position from said second position.

4. :The method of producing a radio frequency equi signal surface for guiding mobile vehicles which consists in radiating radio frequency signals of like frequency from a pair of spaced points, .and producing each of said signals intermittently in repeating cycles of off and on periods with the on periods of both signals of equal duration and the on periods of one signal overlapping the on periods of the other signal.

5. The method of producing a radio frequency .equi-signal surface for guiding mobile vehicles which consists in radiating radio frequency signals of like frequency from a pair of spaced points,

and producing each of said signals intermittently in repeating cycles of off and on periods with the onperiods of both signals of equal duration and signal overlapping the on .thetime duration of the periods in which both signals are radiated is materially different from periods in which one signal only is radiated.

6. A radio beacon system comprising a pair of antennae spaced from each other, means for radiating from said antennae radio frequency signals of like frequency, and means for cyclically interrupting the radiation from each of said anstituting a substantial fraction of tennae tOS-DIOdHCQlGECh of said-signals intermit- -tently-in'repeating cycles of off and on periods with the on periods of one signal overlapping the on periods of'the other signal for a time conthe duration of said periods.

'7. A radio beacon system comprising a, pair of 'antennaetspacedfrom each other, means for radiating fromsaid antennae radio frequency signalsof like frequency, and means for cyclically interruptingwthe-radiation from each of said antennae'tojproduce each of said signals intermittently in repeating cycles of off and on periods with; the on periods of one signal overlapping the on periods of the other signal to such an extent that the time duration of the periods in which bothsignalsare radiated in a substantial fraction of the timeduration of said periods and materially diiferent from the duration of the periods in which onesignal onlyis radiated.

8. A radio beacon system comprising a pair of antennaezspaced fromeach other, means for radiating from said antennae radio frequency signals of like-frequency, and means for cyclically interruptingthe radiation from each of said antennaeto produce each- QfLsaid signals intermittentlyin repeating cycles of off and on periods with the on periods of both signals of equal duration and the on periods of one signal overlapping the on periods of the other signal.

9. A radiobeacon system'comprising a pair of antennae spacedfrom each other, means for radiating fromsaid'antennae radio frequency sig- -nals of like frequency,and meansfor cyclically interrupting the radiation from each of said antennae to.produce 'eachof said signals intermittently in repeating cycles of off and one periods with'theionzperiodsof-both cycles or equal duration-and the on periods of'one signal overlapping 'the on periodsof the other signal to such an extent'that the time duration of the periods in which both-signals are radiated is materially different from-theduration of the periods in which one signal only is radiated.

WILLIAM J. OBRIEN.

REFERENCES CITED The following references are of record in the file v. of this patent: 

